Add word_characters to language overrides & use for more things

Use word_characters to feed completion trigger characters as well and
also recognize kebab as a potential sub-word splitter. This is fine for
non-kebab-case languages because we'd only ever attempt to split a word
with a kebab in it in language scopes which are kebab-cased

Co-Authored-By: Max Brunsfeld <max@zed.dev>

crates/editor/src/test/editor_lsp_test_context.rs

@@ -50,7 +50,7 @@ impl<'a> EditorLspTestContext<'a> {
             language
                 .path_suffixes()
                 .first()
-                .unwrap_or(&"txt".to_string())
+                .expect("language must have a path suffix for EditorLspTestContext")
         );
 
         let mut fake_servers = language